In hard disk drives (HDD), deleterious effects can occur that are known as “adjacent track interference” (ATI), a phenomenon caused by inadvertent erasure of data that is underneath certain portions of the recording head during disk drive operation. There are presently no known solutions to this problem, other than to design heads such that ATI effects are minimized, or to adjust the write current and/or the disk design to minimize ATI, but due to process and material variations, a system designed to produce little or no ATI may still exhibit poor ATI performance, that is, cause inadvertent erasure of victim data tracks in the drive. Generally, ATI is not a serious issue in the short term for nominally good head designs, but repeated use of the head in the drive causes gradual performance degradation over time because data on adjacent tracks is increasingly erased as the head is used.
The present invention further recognizes that conventionally, ATI has been understood to occur to tracks (“victim tracks”) that are immediately next to a track being written (“aggressor track”) in hard disk drives that employ skewed heads, e.g., in drives that use rotary actuators which produce large head skews relative to the track near the outer diameter (OD) of a disk. As critically recognized herein, however, heretofore unknown ATI can occur at zero skew and to victim tracks that are relatively distanced from the aggressor track, e.g., that may be as much as two microns distant from the track being written for hears designed for track pitches of two hundred nanometers (200 nm) or less. Prior solutions to detecting ATI for corrective action thus were not directed to such distant victim tracks and, hence, were not designed to detect it, despite the fact that the present invention understands it exists. Having made this discovery, the present invention further understands that it is important to detect and characterize this previously unknown failure mode.